In recent years optical fibers have come into wide spread use in a wide variety of applications in which optical signals are transmitted along such fibers and are switched from one optical fiber to another using an optical switch system. Optical switches generally include structure to support fiber positioning, alignment signal emitters and interconnected computer control electronics. A fiber positioning structure is provided near the end of each fiber to selectively point the end of a fiber to one fiber group toward the end of a selected fiber in another fiber group to provide switched optical transmission between the two fibers. Examples of optical switches are shown in U.S. Pat. Nos. 4,512,036 and 5,177,348.
Movable mirrors having torsional hinges are may be used as the switching device in such optical switching systems to reflect, route, and/or attenuate light of the optical signals. However, the durability and life span of current torsion-hinge movable mirror devices have suffered due to failures in the torsional hinge that allows pivoting of the devices. Such failures are at least partly because the torsional hinge of the mirror devices often experience stress due to different coefficients of expansion between the silicon mirror and the support structure on which the mirror is mounted. In other words, temperature variations may cause a hinge of the movable mirror device to experience compression and possibly even tension forces due to different coefficients of expansion of the device components. Since such stresses may cause the failure of these devices, there is a need for reducing or eliminating such unwanted or unintended stresses experienced by the hinges of a torsion-hinge movable mirror device.
Texas Instruments presently manufactures a two-axis analog mirror MEMS device fabricated out of a single piece of material (such as silicon, for example) typically having a thickness of about 100-115 microns. The layout consists of an oval mirror (normally about 3.8 mm×3.2 mm) supported on a gimbal frame by two silicon torsional hinges. The gimbal frame is attached to a support frame by another set of torsional hinges, and the support frame is mounted to a support structure that may be manufactured from a ceramic or plastic material which has a coefficient of expansion different than the silicon. A similar single axis mirror MEMS device may be manufactured by eliminating the gimbal frame, and hinging the mirror directly to the support frame.